This invention relates to polymeric acetal carboxylic acids and acid salts and mixtures of either of these with the corresponding salts which are useful for the reversible deflocculation of clay slurries.
Clays are generally considered to be a group of aluminosilicate minerals of varying crystallinity which naturally occur as plastic, soft, variously colored earths. In many clays, about 30 percent by weight of the solid particles have a diameter less than about 0.002 millimeters. Such clays are widely used for the manufacture of ceramics for industrial and domestic uses. Of the various clays, typical examples include kaolin, montmorillonite, halloysite, bentonite and the like.
In the mining of various clays, such as kaolin, the clay is contacted with water and a small amount of a deflocculating agent, such as tetraalkali metal pyrophosphate, alkali metal tripolyphosphate and the like, to form a thin slurry of the clay in water. The slurry can be thickened again by reducing the pH to cause the clay to reflocculate.
Although satisfactory results are achieved by the prior art processes, it has now been found that clays can be deflocculated by the acetal carboxylic acid polymers of the present invention to produce thin slurries, which will reflocculate without further treatment after a time interval which time can be controlled by the proper selection of the initial pH and the end groups at the termini of the acetal carboxylic acid polymers. Such use of acetal carboxylic acid polymers for the reversible deflocculation of clays is fully described in copending application Ser. No. 156,703, filed June 5, 1980.
The salt forms of polymeric acetal carboxylates were described in U.S. Pat. No. 4,144,226 issued Mar. 13, 1979, and the salt forms can be the precursors to the acetal carboxylic acid polymers of the present invention. Formerly it was believed that such partially or completely acidified polymers in an aqueous environment would hydrolyze so rapidly that the acids and acid salts would have no more than a fleeting existence and would have no apparent utility.
Now it has been surprisingly found that the hydrolytic stability of the acids and acid salts can be sufficiently controlled by the selection of end groups at the polymer termini so that the polymers can have a significantly long lifetime for useful applications, e.g., in reversible deflocculation of clay slurries. The method for controlling the hydrolytic stability of acetal carboxylate polymers is fully described in copending application Ser. No. 156,706, filed June 5, 1980.
According to the present invention, acetal carboxylic acid polymers are provided which have sufficient hydrolytic stability to be useful for the reversible deflocculation of clay slurries over significantly long time periods. Since such slurries reflocculate as the polymers of the present invention hydrolyze at a controlled rate, there is no need to readjust the pH of the deflocculated clay slurry to initiate reflocculation. Thus it will be seen by those skilled in the art that a significant improvement has been made in the deflocculation and reflocculation of clay slurries using the polymers of the present invention.